1) When you do something good and think its all down to your skill/knowledge or whatever, you just say skillage.
2) Or when someone does something good.
3) In football, When you take it around someone or Skill them you shout SKILLAGE

Brandon: Did you SEE THAT! Oh My God. That was sick.

Steve: Yeh, all you did was take the ball round me, dont be acting like your all hard.